A mass timber office building in Lambeth doubles down on sustainability goals by slashing embodied carbon and incorporating a fully-demountable structure designed to drive reuse instead of demolition. Stephen Cousins reports.
Dante’s description of Paradise in The Divine Comedy is of a celestial realm of increasing spiritual enlightenment. If the pursuit of sustainability is an attempt to take architecture one step closer to that higher plane, then arguably the Paradise SE11 office development in Lambeth, south London, is within touching distance.
The six-storey, 63,250 ft2 office block was designed by architect Fielden Clegg Bradley Studios (FCBS) for developer Bywater Properties, to achieve a new standard for workspace design. The aim was not only for it to become “London’s Healthiest Workspace,” but also to embody the principles of a circular economy and whole-life design.
The hybrid structure, focused on a mass timber frame with cross-laminated timber (CLT) floors and glulam beams, is fully demountable, allowing for reuse in the distant future when the building is no longer fit for purpose.
This contributes to an embodied carbon footprint that is 35% below the RIBA 2030 Climate Challenge target, with over 1,800 tonnes of CO2 sequestered in the frame, making it one of the lowest embodied carbon offices in the UK.
Designing an extensive mass timber building just months after the Grenfell Tower tragedy meant navigating a complex and shifting set of fire requirements, ultimately adapting the strategy for the facade and cores to limit risks.
Proving that the novel connection details and junctions in the demountable structure would be resilient in a fire meant developing a robust method for testing and certifying the structure using full-scale mock ups – in collaboration with specialist sub-contractor B&K Structures.
Ambitious beginnings
Paradise SE11 is located on a hemmed-in site directly alongside the main railway line into Waterloo, just a few minutes walk from the Albert Embankment. It takes its name from Old Paradise Gardens, a small park running alongside.
The height and footprint of the building went through several iterations during planning as the block was progressively flattened to avoid impinging on protected views across Westminster and towards Big Ben.
Simon Richardson, senior associate at FCBS tells ADF: “Every time the building got lower, the footprint had to get bigger, just to make the project viable, now it takes up almost 95% of the site curtilage.”
The initial brief didn’t call for a timber building, but as the architect assessed different options with the structural engineer, it became clear that engineered wood, if used throughout, could potentially offset most of the embodied carbon and operational emissions.
Bywater got on board with the concept, however the extent of the ambition for timber were impacted by the Hackitt Review of Building Regulations and fire safety in 2018, following Grenfell, bringing concerns over fire risks to the fore.
During the design process, it was a case of “working backwards” from the position of a fully mass timber building with a “heightened focus on non-combustible materials,” and a plan to thoroughly test any combustible structures to ensure safety, says Richardson.
Chunky glulam columns and beams and CLT floor slabs make up the majority of the building structure. Supporting columns run from ground to fifth floor through the middle of the building and from ground to second floor around the perimeter.
Steel columns are used above the second floor around the perimeter, as part of a drive to eliminate combustible materials from the facade, as well as provide support for the horizontal glazing.
Concrete was omitted from the scheme almost entirely, apart from in the two stair and lift cores, where a proposed all-timber solution was considered “one innovation too far” by the fire services, says Richardson. Resorting to concrete for the cores ensures a robust two hour enclosure rating, and according to the architect, this strategy gave fire services the confidence to permit other, higher risk elements in the building.
Close proximity to the railway line put a particular focus on combustibility of the facade, so early doors the design team had close liaison with rail services, listing out all the materials to ensure there was nothing combustible.
According to Richardson, this wasn’t a requirement of legislation, but came from a need to bolster the mass timber strategy and demonstrate zero risk from the facade to the railway and the building. Even where the timber slabs project into the exterior wall build up, they are encased in a fire protection board to guarantee firestopping.
The facade is clad with two types of teal-coloured terracotta tile – a nod to Lambeth’s Royal Doulton heritage – one extruded, one featuring a unique pattern co-designed with the input of local schoolchildren under the guidance of social enterprise MATT+FIONA. The childrens’ tiles are applied in bands around the windows on level two.
The greenish tint of the facade is a fitting backdrop to the park, where a Grade II-listed brick boundary wall was entirely dismantled and rebuilt as part of the project, complete with repositioned headstones.
Calculating carbon
Keeping track of embodied carbon was critical for a building that’s striving to be an exemplar of sustainability for the sector.
During early design, Paradise was a test case for Fielden Clegg Bradley’s new carbon calculation tool FCBS Carbon, which is designed to to help architects estimate and reduce the whole-life carbon emissions of a building proposal.
“The tool is focused on comparative design, enabling users to compare one design against another to see the different playoffs for carbon,” says Richardson, adding that further along in the design process, other carbon calculation tools were introduced to measure the full embodied carbon life cycle.
Material choices were constantly challenged and embodied carbon was a key criteria used to ensure emissions thresholds were not exceeded. Associated requirements were also built into the tender bidding process to ensure targets were adhered to onsite.
Efforts to limit embodied carbon weren’t always successful. For example, the design team proposed to install a reused raised access floor saved from demolition to cut upfront carbon by roughly 8-10%. However, the agents were concerned about ‘sellability’ of the solution, which represented a significant cost uplift over new raised access floors, which were ultimately specified.
According to calculations using the software (One Click LCA*2), the project limited upfront carbon emissions (including material manufacturing, transportation, construction, and other phases, excluding renovation and disposal) to 413 kg CO2e per square metre of floor area.
This represents an approximate 60% reduction compared to the benchmark 1,000 kg CO2e/m2 for new office buildings set by the Greater London Authority. Paradise sequesters over 1,800 tonnes of CO2, equivalent to building 24 homes.
For comparison, Waugh Thistleton’s 5,000 m2 Black & White Building, completed in 2022, came in at 410 kg CO2e/m2.
Reducing whole lifecycle emissions is vital to help buildings underpin national net zero targets, but what about 60, 70 or 100 years down the line? What can be done to ensure that buildings aren’t simply knocked down and sent to landfill?
An important piece of the puzzle is to design them with a high level of circularity so that structures, products and materials can be easily dismantled and reused at end of life, retaining their value.
Paradise’s pioneering approach to design for disassembly required close collaboration between the architects, engineers, and consultants. It hinges on a strategy to exploit dry mechanical fixings and reversible fastenings, instead of adhesives, that allow components to be easily demounted in the future. About 80% of the structural wood is designed for reuse after the building’s demolition.
Logical breakdown
All components were designed for logical and practical disassembly. Achieving this at interfaces between different materials, such as where steel columns interface with CLT floor slabs, was a particular challenge. Traditionally, cementitious grout would be used in connections to ensure firestopping, instead the team looked at alternative options to grouts – ultimately adopting a combination of stone wool and sealants.
CLT floor build-ups conventionally rely on a cast-in coating of cementitious screed to protect the timber, and ensure acoustic and fire performance. Instead, Paradise features lightweight cementitious boards laid on top of the floors, which, thanks also to novel connection details, can be easily taken up in future.
The disassembly strategy extends to the cladding, says Richardson: “The ceramic is dry fit, it is also hard wearing and self-cleaning, due to proximity to the railway system, helping minimise maintenance.” The tiles are manufactured to last 100 years. The general move away from adhesives, to enable a demountable structure, also contributed to efforts to eliminate all VOCs from the building, helping support an anticipated WELL Gold accreditation.
The prevalence of non-standard details, alongside extensive use of timber throughout the building, demanded the construction of a full-scale mock-up for fire testing to ensure everything was compliant with building regs and would function as intended.
“Significant testing was needed to demonstrate that the timber will ‘self-extinguish,’ as part of the fire strategy,” says Richardson, “We built a mock-up of a one bedroom studio over two floors, including the glulam columns and all the connection details, then monitored it as it was burnt.”
While most of the structure performed as anticipated, some of the connection jointing was adjusted to ease installation and to eliminate a small gap that occurred due to the tight tolerances.
According to the architect, researching, procuring and carrying out the tests was a “very costly exercise,” but the project was fortunate to have financial backing from Japanese logging and timber processing company Sumitomo Forestry, which became interested in the project during the planning stages and wanted to help support innovation in timber buildings. The company ended up forming a 50/50 joint venture with Bywater Properties to develop the scheme.
“Lots of projects don’t go ahead because there has not been the investment to enable the testing, so we were very lucky to have Sumitomo onboard,” says Richardson, “Now Bywater has committed from first principles to look to use timber and test if it’s the most practical options for every project it does.”
With reuse now built into the building’s DNA, the question is how to ensure that any future developers of the site make use of the structure and actively disassemble it rather than simply knocking it down?
“This building could last 100 years and disassembly is already a growing industry, in 30, 40 or 50 years it’s going to be much more commonplace,” concludes Richardson, “The most helpful enabler for that process was making it a design constraint from day one.”